1. Technical Field
This invention relates to compressible fabric substrates, in particular those containing a plurality of closed cells therein, for use in composite structures such as printing blankets, gaskets, packing materials, flexible diaphragms and the like.
2. Description of Related Art
Although not limited to use in printing blankets, the development of the present invention is particularly adaptable to printing blankets, and thus the history of improvements made to such printing blankets to increase their compressibility is applicable to the present invention.
Early printing blankets used in connection with rotary printing operations consisted of a fabric substrate backing layer bonded to a rubber printing face (see, e.g., U.S. Pat. No. 2,099,024 to Lewis). Problems with these early blankets stemmed from the fact that rubber is non-compressible when confined. Thus, when pressure was applied to the non-compressible rubber surface, the rubber would distort and cause uneven rolling waves at the nip, i.e., the point between the printing blanket and the impression cylinder. Such distortions would cause ink smearing and compression of the textile backing. Further, repeated compression of rubber blankets during the printing operation tended to cause permanent impressions in the blanket and irreparable damage to the textile backing.
In an attempt to solve many of the aforementioned problems, compressible printing blankets were developed. Compressible blankets today generally consist of a multi-ply fabric substrate base with a compressible cellular layer or layers and a vulcanized elastomeric face. One such compressible blanket is described in U.S. Pat. No. 3,147,698 to Ross. In that patent, the compressible layer is formed by impregnating a highly porous felted fibrous web with an elastomeric material in a solution or water dispersion, such as a natural rubber latex, followed by curing the web under such conditions that it retains a high degree of porosity. Thus, a large volume of minute voids or air spaces were obtained in the finished sheet to constitute the compressible layer which is responsible for the compressibility property of the web.
Subsequent improvements in offset printing blankets to date have been directed toward achieving the desired properties of volume compressibility, resistance to lateral distortion and sufficient firmness, i.e., the resiliency to "spring back" after use. A blanket having all these properties may be formed by gluing together several layers of material with an adhesive, with each layer possessing one or more of the desired properties. Typically, a layer of firm, non-extensible woven material is used to provide resistance to circumferential and lateral distortion of the blanket. Compressibility and resiliency have been achieved by selecting layers having such characteristics in the construction of the blanket.
One such development is disclosed in U.S. Pat. No. 4,042,743 to Larson. In that patent, the compressible layer is sandwiched between one or more layers of fabric. The compressible layer is made by incorporating resin microballoons in suitable proportions in an elastomer. Incorporation of such balloons in the compressible elastomeric layer imparts a fine-celled structure of closed cells.
Another method of producing such a closed cell or partially closed cell rubber containing microballoons is described in U.S. Pat. No. 3,219,600 to Rucker.
Similar uses of microballoons or hollow microspheres in the compressible layers of printing blankets are disclosed in U.S. Pat. Nos. 3,700,541 to Shrimpton et al, 3,983,287 to Goossen et al, and 4,770,928 to Gaworowski et al. In these patents, hollow microballoons are impregnated in a resilient polymer or the like to form a compressible elastomeric sheet for use as an intermediate layer in a printing blanket.
It is also known by U.S. Pat. No. 2,885,303 to Kaplan that microballoons can be adhered to the yarns or threads of a fabric, but not to the spaces therebetween, by use of a binder or lacquer containing same to form a breathable fabric.